Mesonychia

Mesonychia Temporal range: Early Paleocene–Early Oligocene PreЄ Є O S D C P T J K Pg N
Harpagolestes immanis skull
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Superorder:	Laurasiatheria
Clade:	Scrotifera
Clade:	Ungulata
Order:	†Mesonychia
Families
†Hapalodectidae †Mesonychidae †Triisodontidae

†Hapalodectidae
†Mesonychidae
†Triisodontidae

Mesonychia ("middle claws") is an extinct taxon of small- to large-sized carnivorous ungulates related to the cetartiodactyls. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely when the last genus, Mongolestes, became extinct in the early Oligocene. They resembled wolves, albeit superficially. Early mesonychids probably walked on the flats of their feet (plantigrade), while later ones walked on their toes (digitigrade). These later mesonychids had hooves, one on each toe, with four toes on each foot.

Mesonychids probably originated in Asia, where the most primitive mesonychid, Yangtanglestes, is known from the early Paleocene. They were also most diverse in Asia, where they occur in all major Paleocene faunas. Since other carnivores, such as the creodonts and condylarths, were either rare or absent in these animal communities, mesonychids most likely dominated the large predator niche in the Paleocene of Asia.

One genus, Dissacus, had successfully spread to Europe and North America by the early Paleocene. Dissacus was a jackal-sized carnivore that has been found all over the Northern Hemisphere, but its daughter genus, Ankalagon, from the early to middle Paleocene of New Mexico, was far larger, growing to the size of a bear. Species of the later genus, Pachyaena, entered North America by the earliest Eocene, where they evolved into huge species surpassing even Ankalagon in size. Mesonychids in North America were by far the largest predatory mammals during the early Paleocene to middle Eocene.